Spectral
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USB power drop on RPv2

Thu Jan 17, 2013 12:45 pm

Hi all. ;)
Raspberry pi v2. Power supply 1200mA from RS. On usage 7 days. Working good, then.. Have problem with power on USB connected:
Voltage on jack: 5.00 - 5.05V all time. Max 450 mA used.
Voltage on TP1-TP2
- booting : 4.8V
- USB driver activate (onboard ethernet): 4.64V
- mice\key connected: 4.60V (optional)
then internal USB hub down, voltage up to 4.74V
Can not use lsusb without network\keyboard. Trying PC PS with 5V 20A line. Is same.
Please, help. :cry:

obcd
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Re: USB power drop on RPv2

Thu Jan 17, 2013 3:17 pm

You should check the voltage drop over the main polyfuse. It will probably increase when you add usb items.
You can power the Pi over 2 of the GPIO pins, or you can short that polyfuse. (This will void your warranty)
You need at least 4.85V between TP1 and TP2 for a stable operation.
Some people will say you can go lower.
The current that goes to usb devices also passes trough that polyfuse. If you power on the gpio connector, the fuse is bypassed.

Spectral
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Re: USB power drop on RPv2

Thu Jan 17, 2013 4:10 pm

On polyfuse voltage drop -0.67V with 2(40mA+30mA) devices attached.
I must return it for warranty repair? Replace of polyfuse cost less.
GPIO2 (pin3) must be in input mode?

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rurwin
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Re: USB power drop on RPv2

Thu Jan 17, 2013 4:16 pm

If you have measured the voltage at the jack on the RaspPi, then it is the polyfuse. But it does not go bad magically. Try switching the RaspPi off for 24 hours. It may recover.

Spectral
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Re: USB power drop on RPv2

Thu Jan 17, 2013 5:39 pm

Ok, i try. I'll write about the results in a day.
But on a daily basis, it will have to turn off once a week, or is this a one-time?

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mahjongg
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Re: USB power drop on RPv2

Thu Jan 17, 2013 6:13 pm

If you drive more that 1.1A through the polyfuse it will start to increase its resistance (in an attempt to limit the current), and when you leave it be it will slowly return to, but never reach, (as theoretically that would take "forever") its initial value. But except for driving current through it the polyfuse is also affected by high temperatures, so if it has been affected by high temperatures for an extended time it may also exhibit higher than normal resistance values. The "specified" value is the value as it is after being soldered with the normal "profile" (temperature curve).

Spectral
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Re: USB power drop on RPv2

Thu Jan 17, 2013 6:29 pm

Strange, that he began to increase their resistance. The unit does not heat up. Current consumption of no more than 450 - 500 mA (with power supply).
It could be that polyfuse defective?

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mahjongg
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Re: USB power drop on RPv2

Thu Jan 17, 2013 6:33 pm

If its initial resistance is abnormal, it will also trip at a lower current.
So if it has ever "tripped" or exposed to heat in the past and never got enough time to recover, it may still behave abnormally now, and each time you allow it to again "trip" it will become "more abnormal".

Most people don't know it but if you put a power supply on it that has an output that can run up to more than 5.6Volt unconnected, and then plug it into the PI that high voltage may trip the over-voltage protection device on the PI which will short that voltage, which will probably cause a short current to flow through the polyfuse that causes it to trip. After that, and not waiting enough days for the polyfuse to recover the polyfuse may start behaving this way.
That may, or may not, have happened in your case.
It could also be that while soldering the board an "accident" happened that heated up the polyfuse more than normal, but its impossible to say that that happened in this case.
I would say, try to exchange this PI for another one, under a hopefully lenient compensation scheme.

Spectral
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Re: USB power drop on RPv2

Sat Jan 19, 2013 5:03 pm

Spectral wrote:Ok, i try. I'll write about the results in a day.
48 hr powered-off has no effect.
4.65V at TP1-2, 5V at power jack.
Need to send in for repair?

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mahjongg
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Re: USB power drop on RPv2

Sun Jan 20, 2013 1:08 am

a real recovery time for a polyfuse is counted in weeks rather than days, especially if there have been multiple "fuse blow" actions shortly after each other.
In fact according to scientific principles such a fuse will never totally recover, so if the problem is really the polyfuse (and that can be established by measuring the voltage across the polyfuse while a normal current is running through it) then you might as well try to return it under guarantee.

Terranigmus
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Re: USB power drop on RPv2

Mon Jan 21, 2013 8:28 pm

What might cause this? I first used a 500 mA mobile power adapter and Ethernet+USB dropped, now I am trying a 2A power adapter and it drops even faster.

What can I do?

mpalomer
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Re: USB power drop on RPv2

Tue Jan 22, 2013 4:50 am

I'm having a similar problem with mine. It was working fine for a while (had USB WiFi up long enough to update everything and do some other setup tasks over SSH) the first day I had it. After that, USB went out, and each time I try to use it, any USB devices lose power after just ~2-3 minutes. I've tried this with even just a 100mA keyboard plugged in, with just a USB stick plugged in, with 2 different power adapters, and with 2 different distros, and the result is always the same: it works for 2 minutes, then any USB devices lose power but the Pi keeps running. I'm almost certain it has something to do with the F3 fuse (though unfortunately I have no way of confirming this as my DMM decided to stop reading voltages this weekend...).

My question is: if the problem is the F3 polyfuse being blown from the first day when I was using USB WiFi (a stupid choice, gonna have to get a powered USB hub), should I just wait a certain amount of time for the polyfuse to recover so I can use it again, or should I try to return it for a new one? How long should I wait to try it again? I've been reading about the polyfuse issues with the Pi, and I haven't found a straight answer as to whether it's a permanent defect (in which case I should just return it) or if it's something it can recover if I just wait long enough.

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rurwin
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Re: USB power drop on RPv2

Tue Jan 22, 2013 10:08 am

The reason you haven't seen any clear answers is that there aren't any; the variables involved with the history of the polyswitch fuse, the draw from the USB, how often the Pi is switched on and how long it rests between, what USB devices are connected and when, are all interrelated in a highly complex fashion.

Here is everything you need to know about how polyswitch devices work.
Tyco Electronics wrote:... we can clearly see that even after a number of hours the device resistance is still greater than the initial resistance. Over an extended period of time, the resistance will continue to fall and will eventually approach the initial resistance.However, since this time can be days, months, or years, it is not practical to expect that the device resistance will reach the original value for operational purposes. Therefore, when PolySwitch devices are being developed, this "trip jump" or "reflow jump" is taken into consideration when determining the hold current. This increase in resistance is defined as R1MAX and is measured one hour after the thermal event. It should be noted that these trip jumps are non-cumulative over sequential trip events.
Which means that even many trips over an extended period should not cause a problem. The polyswitch should be back in spec within 1 hour. My feeling is that for whatever reason, and it might be just that the input voltage is below 5V, the non-trip increase in resistance (see figure 3) is sufficient to cause your USB devices to fail. You should measure the voltage either side of the polyswitch with respect to TP2. If the higher of the two voltages are below 4.75V, or rather close to it, investigate a new USB cable or PSU. If the lower voltage is below 4.75V then it may cause problems with the USB devices, especially if you are using a PS/2 keyboard with a USB adapter. However USB devices should work with voltages down to 4.4V. The difference between the values should be no more than 0.2V, or maybe 0.3V if you are working the Pi very hard and using thirsty USB devices; if it is more then you have a faulty unit. (See this TE document. I believe F3 is a microSMD-075 or a close equivalent, with a maximum (R1MAX) resistance of 0.4 ohms.)

It may be instructive to invest in some freezer spray and cool just F3 at 30 second intervals. If that stops your USB devices dying it means F3 is the cause of the problem. It doesn't mean that it is faulty though; the problem could be that something else is out of spec, making F3 more critical.

monkmaniac
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Re: USB power drop on RPv2

Fri Feb 01, 2013 5:03 am

Just chiming in to say I've had a similar problem: 5.09v one side of F3, 4.63v on the other (and between TP1 and TP2).

I noticed the problem while testing webcams today...the Pi would apparently freeze up after grabbing a few frames (I was remotely accessing the Pi) and the webcam light would go out. Later the same freezing would occur with no webcam but with a wifi adapter attached.

I tried the webcam tests with a second Pi and it worked flawlessly, lowest voltage was 4.75v. I suppose I'll just wait and see if the polyfuse behaves in a few days...did anyone else have luck w/ waiting?

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